The field of this invention relates to techniques for cutting and removing casing in a single trip, particularly through subsea wellheads.
Typical completions involve multiple casing sizes concentrically mounted and supported in a wellhead, with each section having a seal assembly in the wellhead. Govenment regulations require removal of wellheads when the well is no longer in service. Procedures for accomplishing the removal of the wellhead would involve an initial trip to cut the innermost section of casing using a marine swivel which is supported by the wellhead. The marine swivel allows the string with a cutter to rotate while the exterior of the swivel remains stationary so that it can be supported by the wellhead. At the conclusion of this step with the innermost section of casing cut, the cutter is removed and the seal puller is installed. It is run into the wellbore for a second trip to pull the seal for the innermost casing. Thereafter, a third trip is made with a spear to grab the cut casing segment and bring it up out of the well to the surface. This procedure can be repeated to then remove the next casing section that is exposed. Each time the seal puller needs to be a different size to accommodate the specific casing section being removed. In the event all the casing sections are to be cut, the removal of the seals for each casing size is not necessary since they will all be removed together.
There are several known spear designs on the market, such as those now produced by Baker Oil Tools and referred to as type B, C, D or E. These designs have exposed grapples so that if they are rotated, they will tend to come out radially. Accordingly, such known prior designs of spears could not be combined with a single- or multiple-string cutter because they would snag in the casing as the cutter tried to rotate.
Designs of marine swivels are also known. One such product is made by Baker Oil Tools and identified as product No. 170-01. These marine swivels can be adapted to support a seal-pulling assembly of different sizes to accommodate the sequential removal of casing sections from the wellbore in discrete 3-trip operations in the prior art.
The limitations of some of the spears of the prior art also included a weight-set feature which would make them sling out with the application of centrifugal force. This, again, would detract from their use in conjunction with any kind of cutter involving rotation.
Accordingly, the objects of the invention are to reduce rig time, thug saving the well owner significant quantities of money by making in one trip what has previously been done in the prior art in three trips. Another object of the invention is to combine in one string a cutter of whatever type, a spear of whatever type, and seal puller of whatever type so that in one trip with these components properly spaced out, the casing section or sections can be cut, the seal assembly pulled, and the casing section grappled for removal. Another object of the invention is to improve the cutting technique with an improved actuation system for a multiple string cutter which involves longitudinal piston movement moving the cutter in an arcuate motion outwardly for the cut. Another objective is to provide wear surfaces on the cutter elements so that they can be redressed for reuse. Another objective is to provide improved stabilizers which are hydraulically actuated in the preferred embodiment to improve the cutting speed and precision. Yet another objective of the present invention is to design the spear so that the gripping members or slips are protected and cannot engage the casing as the cutter is rotated.
These objectives of the present invention will become more readily apparent to those skilled in the art from a review of the preferred embodiment described below.
A one-trip system for removing casing from a wellhead is described. The string includes a cutting device spaced at the required depth and a grappling device above it at the appropriate location. A swivel tool, such as a marine swivel, is used in conjunction with a seal-pulling assembly so that after cutting the casing, the seal assembly can be pulled without an additional trip into the well. The grappling device or spear can be hydraulically actuated to grab the casing for removal from the wellbore. The spear features a drop-in restrictor which allows sufficient flow during cutting operations with a mechanical cutter without actuating the spear, while at the same time allowing actuation of the spear by circulation after dropping in the restrictor after the casing section has been cut.